A document handler, also known as Constant Velocity Transport (CVT) device, draws individual sheets from a stack of sheets and sequentially allows the image on each sheet to be scanned by an optical module. The above differences must be periodically compensated for in order to ensure consistent imaging over time. One common source of long-term performance variation over time can be attributed to platen and CVT scanning, due to illumination intensity changes (depth of illumination) and sensor changes. The process of periodic compensation is referred to as calibration. The position on the calibration strip of the calibration function is important but difficult to determine on the calibration strip, especially for an internal second side scanner. The teachings hereof are directed to scanner calibration using a calibration strip.